Re: [PATCH V11 05/17] riscv: qspinlock: Add basic queued_spinlock support

[Leonardo Bras <leobras@redhat.com>]

On Fri, Sep 15, 2023 at 10:10:25AM +0800, Guo Ren wrote:
> On Thu, Sep 14, 2023 at 5:43 PM Leonardo Bras <leobras@redhat.com> wrote:
> >
> > On Thu, Sep 14, 2023 at 12:46:56PM +0800, Guo Ren wrote:
> > > On Thu, Sep 14, 2023 at 4:29 AM Leonardo Bras <leobras@redhat.com> wrote:
> > > >
> > > > On Sun, Sep 10, 2023 at 04:28:59AM -0400, guoren@kernel.org wrote:
> > > > > From: Guo Ren <guoren@linux.alibaba.com>
> > > > >
> > > > > The requirements of qspinlock have been documented by commit:
> > > > > a8ad07e5240c ("asm-generic: qspinlock: Indicate the use of mixed-size
> > > > > atomics").
> > > > >
> > > > > Although RISC-V ISA gives out a weaker forward guarantee LR/SC, which
> > > > > doesn't satisfy the requirements of qspinlock above, it won't prevent
> > > > > some riscv vendors from implementing a strong fwd guarantee LR/SC in
> > > > > microarchitecture to match xchg_tail requirement. T-HEAD C9xx processor
> > > > > is the one.
> > > > >
> > > > > We've tested the patch on SOPHGO sg2042 & th1520 and passed the stress
> > > > > test on Fedora & Ubuntu & OpenEuler ... Here is the performance
> > > > > comparison between qspinlock and ticket_lock on sg2042 (64 cores):
> > > > >
> > > > > sysbench test=threads threads=32 yields=100 lock=8 (+13.8%):
> > > > >   queued_spinlock 0.5109/0.00
> > > > >   ticket_spinlock 0.5814/0.00
> > > > >
> > > > > perf futex/hash (+6.7%):
> > > > >   queued_spinlock 1444393 operations/sec (+- 0.09%)
> > > > >   ticket_spinlock 1353215 operations/sec (+- 0.15%)
> > > > >
> > > > > perf futex/wake-parallel (+8.6%):
> > > > >   queued_spinlock (waking 1/64 threads) in 0.0253 ms (+-2.90%)
> > > > >   ticket_spinlock (waking 1/64 threads) in 0.0275 ms (+-3.12%)
> > > > >
> > > > > perf futex/requeue (+4.2%):
> > > > >   queued_spinlock Requeued 64 of 64 threads in 0.0785 ms (+-0.55%)
> > > > >   ticket_spinlock Requeued 64 of 64 threads in 0.0818 ms (+-4.12%)
> > > > >
> > > > > System Benchmarks (+6.4%)
> > > > >   queued_spinlock:
> > > > >     System Benchmarks Index Values               BASELINE       RESULT    INDEX
> > > > >     Dhrystone 2 using register variables         116700.0  628613745.4  53865.8
> > > > >     Double-Precision Whetstone                       55.0     182422.8  33167.8
> > > > >     Execl Throughput                                 43.0      13116.6   3050.4
> > > > >     File Copy 1024 bufsize 2000 maxblocks          3960.0    7762306.2  19601.8
> > > > >     File Copy 256 bufsize 500 maxblocks            1655.0    3417556.8  20649.9
> > > > >     File Copy 4096 bufsize 8000 maxblocks          5800.0    7427995.7  12806.9
> > > > >     Pipe Throughput                               12440.0   23058600.5  18535.9
> > > > >     Pipe-based Context Switching                   4000.0    2835617.7   7089.0
> > > > >     Process Creation                                126.0      12537.3    995.0
> > > > >     Shell Scripts (1 concurrent)                     42.4      57057.4  13456.9
> > > > >     Shell Scripts (8 concurrent)                      6.0       7367.1  12278.5
> > > > >     System Call Overhead                          15000.0   33308301.3  22205.5
> > > > >                                                                        ========
> > > > >     System Benchmarks Index Score                                       12426.1
> > > > >
> > > > >   ticket_spinlock:
> > > > >     System Benchmarks Index Values               BASELINE       RESULT    INDEX
> > > > >     Dhrystone 2 using register variables         116700.0  626541701.9  53688.2
> > > > >     Double-Precision Whetstone                       55.0     181921.0  33076.5
> > > > >     Execl Throughput                                 43.0      12625.1   2936.1
> > > > >     File Copy 1024 bufsize 2000 maxblocks          3960.0    6553792.9  16550.0
> > > > >     File Copy 256 bufsize 500 maxblocks            1655.0    3189231.6  19270.3
> > > > >     File Copy 4096 bufsize 8000 maxblocks          5800.0    7221277.0  12450.5
> > > > >     Pipe Throughput                               12440.0   20594018.7  16554.7
> > > > >     Pipe-based Context Switching                   4000.0    2571117.7   6427.8
> > > > >     Process Creation                                126.0      10798.4    857.0
> > > > >     Shell Scripts (1 concurrent)                     42.4      57227.5  13497.1
> > > > >     Shell Scripts (8 concurrent)                      6.0       7329.2  12215.3
> > > > >     System Call Overhead                          15000.0   30766778.4  20511.2
> > > > >                                                                        ========
> > > > >     System Benchmarks Index Score                                       11670.7
> > > > >
> > > > > The qspinlock has a significant improvement on SOPHGO SG2042 64
> > > > > cores platform than the ticket_lock.
> > > > >
> > > > > Signed-off-by: Guo Ren <guoren@kernel.org>
> > > > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > > > > ---
> > > > >  arch/riscv/Kconfig                | 16 ++++++++++++++++
> > > > >  arch/riscv/include/asm/Kbuild     |  3 ++-
> > > > >  arch/riscv/include/asm/spinlock.h | 17 +++++++++++++++++
> > > > >  3 files changed, 35 insertions(+), 1 deletion(-)
> > > > >  create mode 100644 arch/riscv/include/asm/spinlock.h
> > > > >
> > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > > index 2c346fe169c1..7f39bfc75744 100644
> > > > > --- a/arch/riscv/Kconfig
> > > > > +++ b/arch/riscv/Kconfig
> > > > > @@ -471,6 +471,22 @@ config NODES_SHIFT
> > > > >         Specify the maximum number of NUMA Nodes available on the target
> > > > >         system.  Increases memory reserved to accommodate various tables.
> > > > >
> > > > > +choice
> > > > > +     prompt "RISC-V spinlock type"
> > > > > +     default RISCV_TICKET_SPINLOCKS
> > > > > +
> > > > > +config RISCV_TICKET_SPINLOCKS
> > > > > +     bool "Using ticket spinlock"
> > > > > +
> > > > > +config RISCV_QUEUED_SPINLOCKS
> > > > > +     bool "Using queued spinlock"
> > > > > +     depends on SMP && MMU
> > > > > +     select ARCH_USE_QUEUED_SPINLOCKS
> > > > > +     help
> > > > > +       Make sure your micro arch LL/SC has a strong forward progress guarantee.
> > > > > +       Otherwise, stay at ticket-lock.
> > > > > +endchoice
> > > > > +
> > > > >  config RISCV_ALTERNATIVE
> > > > >       bool
> > > > >       depends on !XIP_KERNEL
> > > > > diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
> > > > > index 504f8b7e72d4..a0dc85e4a754 100644
> > > > > --- a/arch/riscv/include/asm/Kbuild
> > > > > +++ b/arch/riscv/include/asm/Kbuild
> > > > > @@ -2,10 +2,11 @@
> > > > >  generic-y += early_ioremap.h
> > > > >  generic-y += flat.h
> > > > >  generic-y += kvm_para.h
> > > > > +generic-y += mcs_spinlock.h
> > > > >  generic-y += parport.h
> > > > > -generic-y += spinlock.h
> > > >
> > > > IIUC here you take the asm-generic/spinlock.h (which defines arch_spin_*())
> > > > and include the asm-generic headers of mcs_spinlock and qspinlock.
> > > >
> > > > In this case, the qspinlock.h will provide the arch_spin_*() interfaces,
> > > > which seems the oposite of the above description (ticket spinlocks being
> > > > the standard).
> > > >
> > > > Shouldn't ticket-spinlock.h also get included here?
> > > > (Also, I am probably missing something, as I dont' see the use of
> > > > mcs_spinlock here.)
> > > No, because asm-generic/spinlock.h:
> > > ...
> > > #include <asm-generic/ticket_spinlock.h>
> > > ...
> > >
> >
> > But aren't you removing asm-generic/spinlock.h below ?
> > -generic-y += spinlock.h
> Yes, current is:
> 
> arch/riscv/include/asm/spinlock.h -> include/asm-generic/spinlock.h ->
> include/asm-generic/ticket_spinlock.h

I did a little reading on how generic-y works (which I was unaware):

"If an architecture uses a verbatim copy of a header from 
include/asm-generic then this is listed in the file 
arch/$(SRCARCH)/include/asm/Kbuild [...] During the prepare phase of the 
build a wrapper include file is generated in the directory [...]"

Oh, so you are removing the asm-generic/spinlock.h because it's link 
was replaced by a new asm/spinlock.h. 

You add qspinlock.h to generic-y because it's new in riscv, and add 
mcs_spinlock.h because it's needed by qspinlock.h. 

Ok, it makes sense now.

Sorry about this noise.
I was unaware of how generic-y worked, and (wrongly) 
assumed it was about including headers automatically in the build.


> 
> +#ifdef CONFIG_QUEUED_SPINLOCKS
> +#include <asm/qspinlock.h>
> +#include <asm/qrwlock.h>
> +#else
> +#include <asm-generic/spinlock.h>
> +#endif
> 
> So, you want me:
> +#ifdef CONFIG_QUEUED_SPINLOCKS
> +#include <asm/qspinlock.h>
> +#else
> +#include <asm-generic/ticket_spinlock.h>
> +#endif
> 
> +#include <asm/qrwlock.h>
> 
> Right?

No, I didn't mean that.
I was just worried about the arch_spin_*() interfaces, but they should be 
fine.

BTW, according to kernel doc on generic-y, shouldn't be a better idea to 
add 'ticket_spinlock.h' to generic-y, and include above as 
asm/ticket_spinlock.h? 

Or is generic-y reserved only for stuff which is indirectly included by 
other headers? 

Thanks!
Leo

> 
> >
> > > >
> > > > >  generic-y += spinlock_types.h
> > > > >  generic-y += qrwlock.h
> > > > >  generic-y += qrwlock_types.h
> > > > > +generic-y += qspinlock.h
> > > > >  generic-y += user.h
> > > > >  generic-y += vmlinux.lds.h
> > > > > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
> > > > > new file mode 100644
> > > > > index 000000000000..c644a92d4548
> > > > > --- /dev/null
> > > > > +++ b/arch/riscv/include/asm/spinlock.h
> > > > > @@ -0,0 +1,17 @@
> > > > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > > > +
> > > > > +#ifndef __ASM_RISCV_SPINLOCK_H
> > > > > +#define __ASM_RISCV_SPINLOCK_H
> > > > > +
> > > > > +#ifdef CONFIG_QUEUED_SPINLOCKS
> > > > > +#define _Q_PENDING_LOOPS     (1 << 9)
> > > > > +#endif
> > > >
> > > > Any reason the above define couldn't be merged on the ifdef below?
> > > Easy for the next patch to modify. See Waiman's comment:
> > >
> > > https://lore.kernel.org/linux-riscv/4cc7113a-0e4e-763a-cba2-7963bcd26c7a@redhat.com/
> > >
> > > > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
> > > > index c644a92d4548..9eb3ad31e564 100644
> > > > --- a/arch/riscv/include/asm/spinlock.h
> > > > +++ b/arch/riscv/include/asm/spinlock.h
> > > > @@ -7,11 +7,94 @@
> > > >   #define _Q_PENDING_LOOPS (1 << 9)
> > > >   #endif
> > > >
> > >
> > > I see why you separated the _Q_PENDING_LOOPS out.
> > >
> >
> > I see, should be fine then.
> >
> > Thanks!
> > Leo
> >
> > >
> > > >
> > > > > +
> > > > > +#ifdef CONFIG_QUEUED_SPINLOCKS
> > > > > +#include <asm/qspinlock.h>
> > > > > +#include <asm/qrwlock.h>
> > > > > +#else
> > > > > +#include <asm-generic/spinlock.h>
> > > > > +#endif
> > > > > +
> > > > > +#endif /* __ASM_RISCV_SPINLOCK_H */
> > > > > --
> > > > > 2.36.1
> > > > >
> > > >
> > > > Thanks!
> > > > Leo
> > > >
> > >
> > >
> > > --
> > > Best Regards
> > >  Guo Ren
> > >
> >
> 
> 
> -- 
> Best Regards
>  Guo Ren
>